73° 



ZONES AND REGIONS [Pt. Ill, Sect. IV 



altitude where it has already ceased on the windy external margin of 

 the crater. The dependence of the tree-limit on the wind is here most 

 clearly visible. 



The comparison of vegetation in sun and in shade respectively on the 

 Javanese summits is also instructive. The sun-vegetation alone possesses 



Fig. 427. Alpine flora of Java. Vac- 

 cinium myrtoides. Summit of Widodaren, 

 East Java. Natural size. 



Fig. 428. Alpine flora of Java. Coprosma sundana. 

 Summit of Widodaren, East Java. About 3,300 meters. 

 Natural size. 



an alpine habit, for it alone is exposed to those factors of the alpine climate 

 that are here in operation. The retarding action of intense sunlight on 

 growth, and nocturnal radiation, cease in the shade of rocks and shrubs ; 

 the air is calm and moist, so that transpiration remains within moderate 

 limits. Accordingly the plants in sheltered stations possess much larger 

 axes and much more delicate foliage than those in sunny stations. How 

 great the difference can be is clearly shown in Fig. 426, which represents 

 specimens of Gentiana quadrifaria that I found on the summit of the Wido- 

 daren at two closely adjacent but very differently illuminated stations. 



